Patent EA-002412-B1 (EA)
Title: Single well system for mapping of acoustic energy
Inventor: BAILEY JEGGRY R
IPC: G01V1/42
Filed: 1999-02-19
Abstract: 1. Apparatus for locating a source of acoustic waves in the earth, said apparatus comprising: an elongated body having a longitudinal axis and a plurality of segments and being adapted to be connected to a wireline to allow placing said apparatus in a well; a plurality of acoustic receivers comprising separate segments of said elongated body and being attached to said elongated body in a manner that prevents significant torsional deformation of each acoustic receiver with respect to each other acoustic receiver, each of said acoustic receivers including retractable means for exerting a force for clamping said acoustic receiver in said well and having two orthogonal acoustic sensors lying in a plane substantially perpendicular to said longitudinal axis of said elongated body, each of said acoustic sensors adapted to produce an electrical signal in response to an acoustic wave impinging thereon; and electronic means disposed in at least one segment of said elongated body, said electronic means being capable of substantially continuously transmitting said electrical signals to the surface of the earth in real-time. 2. The apparatus of claim 1, wherein said wireline includes one or more fiber optic strands, and wherein said electronic means includes a digitizing circuit to convert said electrical signals to digital signals and a transceiver to convert said digital signals to light pulses for transmission to the surface of the earth over said fiber optic strands. 3. The apparatus of claim 1, wherein said wireline includes one or more copper strands, and wherein said electronic means includes a digitizing circuit to convert said electrical signals to digital signals and a modem to transmit said digital signals to the surface of the earth over said copper strands. 4. The apparatus of claim 1, wherein said apparatus includes at least three acoustic receivers, and wherein at least one of said acoustic receivers includes a third acoustic sensor orthogonal to said two other acoustic sensors. 5. A method for determining the location of a source of acoustic waves in the earth, said method comprising the steps of: placing an apparatus in a well on a wireline, said apparatus including at least two spaced-apart acoustic receivers, each of said acoustic receivers including retractable means for exerting a force for clamping said acoustic receiver in said well and having two orthogonal acoustic sensors lying in a plane substantially perpendicular to the axis of said well, each of said acoustic sensors adapted to produce an electrical signal in response to an acoustic wave impinging thereon, and electronic means for transmitting said electrical signals to the surface of the earth in real-time; clamping said acoustic receivers in said well; using said acoustic sensors to detect said acoustic waves and produce electrical signals in response thereto; transmitting said electrical signals to the surface of the earth; and using said electrical signals at the surface of the earth to calculate the location of said source of acoustic waves. 6. The method of claim 5, wherein said apparatus has a longitudinal axis extending through said spaced-apart acoustic receivers, and wherein said acoustic waves include both P-waves and S-waves, and wherein said step of using said electrical signals to calculate the location of said source of acoustic waves further comprises the steps of: using hodogram analysis methods for both said P-waves and said S-waves to determine the azimuth angle from said apparatus to said source of acoustic waves; using said azimuth angle to define a plane that contains said longitudinal axis of said apparatus and said source of acoustic waves; determining actual time differences between initial arrivals of both said P-waves and said S-waves at said acoustic receivers; estimating traveltime differences for both said P-waves and said S-waves from a plurality of possible source locations within said plane to said acoustic receivers; and selecting as the location of said source of acoustic waves the possible source location for which said estimated traveltime differences most closely approximate said actual time differences. 7. The method of claim 5, wherein said apparatus has a longitudinal axis extending through said spaced-apart acoustic receivers, and wherein said acoustic waves include both P-waves and S-waves, and wherein said step of using said electrical signals to calculate the location of said source of acoustic waves further comprises the steps of: using hodogram analysis methods for both said P-waves and said S-waves to determine the azimuth angle from said apparatus to said source of acoustic waves; using said azimuth angle to define a plane that contains said longitudinal axis of said apparatus and said source of acoustic waves; shifting arrival times of said P-waves and said S-waves at said receivers based on calculated traveltimes from possible source locations in said plane to said acoustic receivers; and selecting as the location of said source of acoustic waves the possible source location that substantially maximizes alignment of said time-shifted P-waves and S-waves. 8. The method of claim 5, wherein at least one of said acoustic receivers includes a third acoustic sensor orthogonal to said two other acoustic sensors, data from said third acoustic sensor being used to resolve ambiguities in the location of said source of acoustic waves.